In a cellular communications network, some or all of the cells may each be divided into two or more sectors. For instance, FIG. 1 illustrates a cell 10 of cellular communications network that is divided into three sectors 12-1, 12-2, and 12-3, which are generally referred to herein as sectors 12. Conventionally, a base station, or Base Station Transceiver Set (BTS), is located at the center of the cell 10 and includes a separate amplifier and antenna for each of the sectors 12. The antennas are so called sector antennas that radiate corresponding beams 14-1 through 14-3 that fill the corresponding sectors 12 without overlapping into adjacent sectors 12. For the conventional base station, there is no power sharing between the power amplifiers for the sectors 12 and, as such, the amplifier for each of the sectors 12 must be designed to satisfy maximum power level demands for the sector 12. In addition, if one of the power amplifiers or the corresponding transmitter fails, the downlink in the corresponding sector 12 is totally lost.
U.S. Pat. No. 7,206,355 entitled DIGITALLY CONVERTIBLE RADIO and U.S. Pat. No. 7,248,656 entitled DIGITAL CONVERTIBLE RADIO SNR OPTIMIZATION each disclose embodiments of a Digitally Convertible Radio (DCR). In one embodiment, the DCR includes multiple parallel power amplifiers and enables power sharing between the power amplifiers such that any one of the power amplifiers is not required to be designed to satisfy maximum sector power level demands. More specifically, FIG. 2 illustrates one embodiment of a DCR 16 according to the teachings of U.S. Pat. No. 7,206,355 and U.S. Pat. No. 7,248,656. As illustrated, the DCR 16 includes a Digital Hybrid Matrix (DHM) 18, an upconversion module 20, a power amplifier module 22 including power amplifiers 24-1 through 24-3, an Analog Hybrid Matrix (AHM) 26, and antennas 28-1 through 28-3 connected as shown. The DHM 18 receives a number of digital transmit signals (S1 through S3) each being for a different sector of a cell. The DHM 18 splits and combines the digital transmit signals (S1 through S3) to generate transformed transmit signals (T1 through T3). Each of the transformed transmit signals (T1 through T3) includes a component of each of the digital transmit signals (S1 through S3). More specifically, as disclosed in U.S. Pat. No. 7,248,656, a first set of complex weights are applied to the digital transmit signals (S1 through S3) and the resulting complex weighted digital transmit signals are combined, or summed, to provide the first transformed transmit signal (T1). Likewise, a second set of complex weights are applied to the digital transmit signals (S1 through S3) and the resulting complex weighted digital transmit signals are combined, or summed, to provide the second transformed transmit signal (T2), and a third set of complex weights are applied to the digital transmit signals (S1 through S3) and the resulting complex weighted digital transmit signals are combined, or summed, to provide the third transformed transmit signal (T3).
The transformed transmit signals (T1 through T3) are upconverted to a desired radio frequency by the upconversion module 20 to thereby provide upconverted transformed transmit signals (T1,UP through T3,UP). The power amplifiers 24-1 through 24-3 in the power amplifier module 22 then amplify the upconverted transformed transmit signals (T1,UP through T3,UP) to provide radio frequency transformed transmit signals (T1,RF through T3,RF). The AHM 26 then splits and combines the radio frequency transformed transmit signals (T1,RF through T3,RF) to thereby generate radio frequency transmit signals (A1 through A3). Notably, the weight sets in the DHM 18 are configured such that the first radio frequency transmit signal (A1) output by the AHM 26 represents the first digital transmit signal (S1) and components representing the second and third digital transmit signals (S2 and S3) in the first radio frequency transmit signal (A1) are minimized and preferably eliminated. In addition, the weight sets in the DHM 18 are configured such that the second radio frequency transmit signal (A2) output by the AHM 26 represents the second digital transmit signal (S2) and components representing the first and third digital transmit signals (S1 and S3) in the second radio frequency transmit signal (A2) are minimized and preferably eliminated and such that the third radio frequency transmit signal (A3) output by the AHM 26 represents the third digital transmit signal (S3) and components representing the first and second digital transmit signals (S1 and S2) in the third radio frequency transmit signal (A3) are minimized and preferably eliminated.
In order to configure the complex weights of the DHM 18, the DCR 16 includes a feedback path including a downconversion module 30, a correlator module 32, and an adaptor 34. The operation of the downconversion module 30, the correlator module 32, and the adaptor 34 and the algorithm for computing the complex weights for the DHM 18 are described in U.S. Pat. No. 7,248,656. In general, as discussed above, the complex weights are configured such that the radio frequency transmit signals (A1 through A3) are output by the AHM 26.
An important benefit of the DCR 16 is that, by using the DHM 18 and the AHM 26, coherent power sharing between the power amplifiers 24-1 through 24-3 is provided. As a result, any one of the power amplifiers 24-1 through 24-3 is not required to be designed to satisfy maximum sector power level demands. In addition, if any one of the power amplifiers 24-1 through 24-3 fails, the DCR 16 is enabled to provide operation in all three sectors, but in a somewhat degraded mode of operation.
One issue with the DCR disclosed in U.S. Pat. No. 7,206,355 and U.S. Pat. No. 7,248,656 is that the DCR must include all resources needed to satisfy future maximum capacity requirements for the cell. Thus, an operator is required to incur significant expense at initial deployment even though initial capacity requirements may be low. As such, there is a need for an improved DCR that addresses this issue.